There is known from the prior art, in particular from EP Patent No. 1 396 766 A1, an electronic analogue display dive watch wherein the current time display hands are also used for displaying dive-related data and in particular the instantaneous depth of the diver. The watch includes for this purpose a pressure sensor for measuring the external ambient pressure, a depth gauge module for calculating the diver's depth as a function of the pressure measurements taken and displaying the calculated depth using one of the hands of the watch.
In the same manner, one could envisage replacing the depth gauge module with a module for calculating an altitude value on the basis of the pressure measurements taken and displaying this calculated altitude by the analogue means of the watch.
However, this kind of altimeter watch has certain drawbacks depending upon the use to which it is put. Indeed, typically during swimming activity, the person wearing the watch regularly moves his arm in and out of the water. Thus, if the altimeter mode is activated, the pressure values measured by the sensor vary greatly each time the medium changes between the air and water. Given that the pressure variation observed when one plunges 10 centimeters into water corresponds approximately to an altitude variation of 100 meters in the air, this type of swimming activity where the swimmer's arm plunges several tens of centimeters into the water with each movement, means that the altitude indication varies by several tens of meters with each of such movements. The analogue display means, although generally attractive and easy to read for the person wearing the watch, in this case have the drawback of having to follow significant altitude variations which results in large movements of the indicator means, such as for example a hand, between a first position corresponding to the real altitude at the water surface and a second position corresponding to an erroneous much lower altitude when the swimmer's arm is underwater. Taking as an example a swimmer swimming in a lake situated at an altitude of 400 meters and a swimming movement periodically taking the swimmer's arm to a depth of 40 centimeters underwater, the analogue altitude indicator will constantly move between the graduations indicating 400 meters (i.e. arm at the surface) and 0 meters (i.e. arm underwater). It would be intolerable for the altimeter mode to operate in this manner. Indeed, on the one hand, the user might doubt that his watch worked properly, given the large movements of the analogue altitude display means in the altimeter mode and, on the other hand, since the analogue display means are controlled by a motor, their jumping back and forth would result in excessive power consumption which is never desirable in a portable instrument.